Comparison of Microleakage of Mineral Trioxide Aggregate Apical Plug Applied by the Manual Technique and Indirect Use of Ultrasonic with Different Powers

Statement of the Problem: A mineral trioxide aggregate (MTA) apical plug is commonly applied prior to endodontic treatment of open-apex teeth. However, difficult application and condensation of MTA in the apical region is a drawback of this technique. Purpose: This study aimed to compare the microleakage of MTA apical plug applied by the manual technique and indirect use of ultrasonic with different powers. Materials and Method: In this in vitro, experimental study, divergent open apices were created in 48 single-rooted, single-canal teeth using ProFile. The teeth were randomly divided into four experimental groups (n=10). All groups received 5-mm thick MTA apical plug at the apical region using one of the following methods. In group 1, MTA was manually condensed while in groups 2-4, indirect ultrasonic energy with minimum, medium, and maximum power levels was used for MTA plug condensation. After setting of MTA, the apical microleakage of the MTA plug was quantified using the fluid filtration method. Data were analyzed using the Mann-Whitney and Kruskal-Wallis tests (p< 0.05). Results: Significant differences were noted in microleakage of MTA plug between the manual group and ultrasonic groups with medium (p= 0.043) and maximum (p= 0.029) power levels. No significant difference was noted in microleakage of other groups (p> 0.05). Conclusion: Considering the current results, it seems that application of MTA with indirect ultrasonic energy at medium or high power level would decrease the microleakage of MTA plug in open-apex root canals.


Introduction
The process of dentin formation and root development stops when an immature tooth undergoes pulp necrosis.
Resultantly, the root canal walls remain thin, and the apex remains open. In such cases, it is imperative to close the apex by artificially inducing the formation of a calcified barrier to allow condensation of root filling materials and improve apical seal. Inadequate apical seal is the most important reason for failure of nonsurgical root canal treatment [1]. Apexification is a commonly used technique to induce the closure of apical foramen in necrotic immature teeth. Single-session apexification by use of an apical plug and formation of an artificial barrier is an alternative to multi-session apexification with calcium hydroxide. In this technique, biocompatible materials are used to create an apical seal and allow root canal filling [1].
Mineral trioxide aggregate (MTA) is among the dental materials proposed for this purpose. MTA has ideal properties such as optimal biocompatibility [2], bacteriostatic activity [3], favorable sealability of the root canal and perforation sites [4] and the ability to set even in presence of blood [5]. The success rate of endodontic treatment of open-apex teeth with a MTA apical plug is reportedly 95.5% [6]. However, difficult application and condensation of MTA in the apical region is a drawback of using MTA for apical plug. Evidence shows that the technique of application of MTA is highly important [6][7]. Indirect application of ultrasonic energy on an endodontic plugger has been recommended for MTA delivery into the root canal to enhance the condensation of MTA in the apical region for formation of an apical plug [7][8][9].
Information regarding an ideal method for delivery and application of MTA into the canal is limited and controversial. Some studies have demonstrated that application of ultrasonic energy during MTA application leads to void formation and results in a filling with lower density and homogeneity compared with manual condensation [10][11]. On the other hand, some other studies have shown that condensation of MTA using ultrasonic energy provides higher compressive strength and higher surface microhardness of MTA compared with manual condensation [9,12]. Another studies indicated that indirect application of ultrasonic energy would improve the adaptation of MTA to dentinal walls [13][14]. Basturk et al. [15] discussed that the compressive strength of MTA, applied by using ultrasonic energy, had no significant difference with that in manual application technique.

Materials and Method
This in vitro, experimental study evaluated 48 singlerooted, single-canal maxillary central incisors with closed apices and no caries, cracks or root curvature.
The selected teeth had been extracted due to different reasons such as hopeless periodontal prognosis.
A total of 48 qualified teeth were randomly divided into four experimental (n=10) and four positive and negative control (n=2) groups. For the purpose of standardization, the teeth were decoronated at the cementoenamel junction using a diamond disc and highspeed hand-piece such that 13±1mm of root length remained. Next, 3mm of the root apex was cut perpendic- In all groups, application and condensation of MTA plug were performed in three steps by application of 2-, 2-and 1-mm thick layers. In group 1, the MTA plug was condensed manually using an endodontic plugger.
In group 2, after the application of each layer of MTA plug, it was condensed by indirect use of ultrasonic energy (Various750-NE134; NSK, Japan) at minimum power level by touching the ultrasonic tip (P10 tip) with the plugger shaft without contacting the tooth walls for 2 s [11,14,17]. In group 3, the MTA plug was condensed by indirect use of ultrasonic energy with the power level of 2.5 (medium) for 2 s. In group 4, the MTA plug was condensed by indirect use of ultrasonic energy at maximum power level for 2 s. It should be noted that the ultrasonic device had minimum, 1, 2, 3, 4, and maximum power levels. Excess MTA on the walls was removed using a #50 stainless steel K-file (Dentsply Maillefer, Switzerland). Immediately after placement of the MTA plug, a radiograph was obtained to ensure its adequate thickness, absence of voids, and optimal adaptation to the canal walls. Next, moist paper points #80 (Ariadent, Tehran, Iran) were placed in the canals.

Results
No microleakage was noted in the negative control group. Severe microleakage was noted through the apex of teeth in the positive control group. Table 1 shows the mean apical microleakage of the experimental groups.
Comparison of microleakage of the groups showed that the amount of microleakage in group 3 (medium ultrasonic power) had a significant difference with that in group 1 (manual condensation) (p= 0.043). Furthermore, microleakage in group 4 (use of maximum ultrasonic power) had a significant difference with that in group 1 (manual condensation) (p= 0.029). No significant difference was noted in microleakage of other groups (different ultrasonic power levels with each other and minimum ultrasonic power and manual condensation) (p> 0.05).

Discussion
Provision of an apical barrier is imperative during cleaning and shaping of root canals to achieve optimal apical seal. In absence of an apical barrier, it would be difficult to prevent the apical extrusion of root filling material and achieve an apical seal. In cases with apical root resorption, apical perforation and necrotic immature teeth, an apical constriction does not exist. In such cases, in order to confine the root filling materials to the canal space, provision of an artificial apical barrier is imperative [18]. Several materials have been proposed for use as apical plug by the researchers such as calcium hydroxide [19], MTA [20] and dentin chips [21]. Of the suggested materials, MTA has a superior marginal adaptation and biocompatibility compared with other materials [22]. Considering the reverse funnel shape of open-apex teeth, we standardized the divergent apical foramen as retrograde using ProFile [40/6%] [23]. Controversy exists regarding the adequate thickness of MTA apical plug [7,[23][24]. Nonetheless, most researc-  [7,25], we indirectly transferred the ultrasonic energy to an endodontic plugger for the condensation of MTA plug.
Aminoshariae et al. [8] showed that direct application of ultrasonic energy for condensation of MTA plug, Parashos et al. [17] showed that MTA condensation and root canal walls, which leads to eventual reduction in microleakage. Yeung et al. [30] showed that using ultrasonic energy for MTA condensation compared with the manual technique increased the weight of MTA mass. Escribano-Escriva et al. [14] indicated that indirect application of ultrasonic energy enhanced the adaptation of MTA plug to the canal walls. Araujo et al. [27] and Friedl et al. [28] stated that ultrasonic energy improved the marginal adaptation of MTA plug to the canal walls and increased its density. Lawley et al. [7] assessed the apical seal provided by the MTA plug after its manual application and by the use of ultrasonic ener- from ours, which may be due to the absence of standardization and absence of any information on minimum and maximum power levels of ultrasonic device. El-Ma'aita et al. [10] stated that use of manual technique resulted in a denser filling compared with the ultrasonic method. In addition, Ghasemi et al. [11] reported that use of manual technique decreased the number of voids in the apical plug [11]. Aminoshera et al. [8] indicated that manual application resulted in superior homogeneity and fewer voids compared with the ultrasonic technique [8].